CDMA2000 is a third-generation (3G) wideband; spread spectrum radio interface system that uses the enhanced service of Code Division Multiple Access (CDMA) technology to facilitate data capabilities, such as internet and intranet access, multimedia applications, high-speed business transactions, and telemetry. The focus of CDMA2000, as is that of other third-generation systems, is on network economy and radio transmission design to overcome the limitations of a finite amount of radio spectrum availability. Several improvements have been added under the CDMA200 framework, and are continuing to be added. One such improvement is high rate packet data (HRPD). HRPD was initially implemented as a single carrier to improve forward link throughput, however it has evolved to a multi-carrier with improved forward and reverse links. The HRPD revision A specifications are contained within the CDMA2000 High Rate Packet Data Air Interface Specification, 3GPP2 C.S0024-A Version 2.0, maintained by the 3rd Generation Partnership Project (3GPP2), which are herein incorporated by reference for all intents and purposes.
The revision A HRPD system employs hybrid Automatic Repeat Request (H-ARQ). H-ARQ is the bit sent on an ARQ channel in response to the 1st, 2nd, and 3rd sub-packet of a reverse-link physical packet to support physical layer ARQ. A method for transmitting broadcast signals using H-ARQ uses a scheme for dividing one encoder packet into a plurality of sub-packets and transmitting the sub-packets using a plurality of slots. A slot is a unit of time equal to 1.667 ms. A receiver receiving the sub-packets performs decoding thereon by combining the sub-packets using an Incremental Redundancy (IR) scheme.
In the reverse link transmission access terminal (AT) protocol, the AT transmits sub-packets to the access network (AN), and the AN responds with an ACK if the AT correctly received the packet or a NAK if the AT incorrectly received the packet. Following receipt of the ACK/NAK, the AT is required to generate either the first sub-packet of the next physical layer packet (if the AT receives an ACK from the AN) or the next sub-packet in sequence for the current physical layer packet (if the AT receives a NAK from the AN).
Regardless of whether the AT received an ACK or a NAK from the AN, the AT is required to transmit the next sub-packet in the sub-frame immediately following the sub-frame containing the ACK/NAK. This places large demands on the AT processor to read the ACK/NAK, determine the next sub-packet to be sent, and prepare the next sub-packet for transmission. Increased processing demands mean that the AT requires a faster or more capable processor. Therefore, what is needed is a means to reduce the processing demands by creating a larger timing window to process ACK/NAK data in reverse link ATs.